```ts
export function mergeIntervals(intervals: number[][]): number[][] {
  if (!intervals.length) return [];

  intervals.sort((a, b) => a[0] - b[0]);

  const merged: number[][] = [];
  let currentInterval = intervals[0];

  for (const nextInterval of intervals.slice(1)) {
    if (currentInterval[1] >= nextInterval[0]) {
      currentInterval = [currentInterval[0], Math.max(currentInterval[1], nextInterval[1])];
    } else {
      merged.push([...currentInterval]);
      currentInterval = nextInterval;
    }
  }

  merged.push([...currentInterval]);

  return merged;
}
```